A scanner is an image-capturing device. Take a conventional platform scanner for example; its basic elements include a glass window for holding a scan object (maybe a document or picture) and an optical module for transforming images to electric signals. The core element of the optical module is an image sensor and a lens for focusing and forming an image on the image sensor. The image sensor (such as charge couple devices; CCD) has many image-sensing pixels, which accumulate electric charges when receiving different light intensities to form voltage differences. Those light intensities are different from those transformed to digital electric signals through an A/D converter. The original digital electric signals can be converted to electronic files. Then users can process image processing, editing, storing, and outputting through computer software.
Refer to FIG. 1 shows the scanning process for a picture from start to finish on a conventional scanner. The description of the process is as follows:
First, confirm that warm up of the lamp is finished (step 11). This step requires some time to enable the brightness of the entire lamp to rise to a stable condition.
Next, AFE (analog front end) data captured by an image capturing front controller are compensated and corrected (step 12). In the conventional art, the AFE can be combined with an image sensor or be present as an independent chip, and the AFE is utilized to convert the analog signal to a digital signal after scanning. This step is to calculate the CCD output-value according to the following equation (1):gain×(CCD output-value+offset)  (1)
Then, perform pixel-shading pixel to pixel (step 13). This step is to compensate the brightness of every pixel to a desired value so that a uniform brightness is reached before scanning. This serves as the standard for compensating the later scanning object.
Start scanning for the targeted object (step 14) after all prior steps have been completed.
Conventional scanners mostly use a cold cathode fluorescent lamp (CCFL). While CCFL has many advantages such as greater brightness, lower electric power consumption, longer service life, and the like, it also has a big drawback. Namely: whenever a user restarts scanner operation, the scanner has to go through a warm up period to enable the brightness of the lamp to reach a stable condition in order to start the scanning of the picture. Hence at step 11, warm up time takes considerable time.
At room temperature the warm up time could last about 1-3 minutes. In colder areas the warm up time is longer. This is quite inconvenient. Some users even mistakenly deem the long warm up time as a machine failure and send the machine back for repairing.
In the present highly competitive environment, how to shorten the waiting time period when the scanner is cold started is an important issue.